Radiation-curing binders and a process for their preparation

ABSTRACT

The invention relates to a process for preparing binders which contain 1) allophanate groups, 2) groups that react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation (radiation-curing groups) and 3) optionally NCO-reactive groups, by reacting at temperatures ≦130° C. A) one or more NCO-functional compounds containing uretdione groups with B) one or more compounds that contain isocyanate-reactive groups and groups that react with ethylenically unsaturated compounds with polymerization on exposure to actinic radiation (radiation-curing groups), and then C) with one or more saturated, hydroxyl-containing compounds other than B), at least one of these compounds having an OH functionality of ≧2, in the presence of D) a catalyst containing one or more zinc compounds, the reaction with compounds C) taking place at least proportionally with the formation of allophanate groups. The present invention also relates to the binders obtained by the process of the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing binders whichcontain allophanate groups, groups that react with ethylenicallyunsaturated compounds with polymerization on exposure to actinicradiation and which optionally also contain isocyanate-reactive groups,to the resulting binders and to their use in coating compositions.

2. Description of Related Art

The curing of coating systems which carry activated double bonds byactinic radiation, such as UV light, IR radiation or electron beams, isknown and is established in industry. It is one of the most rapid curingmethods in coating technology. Coating compositions based on thisprinciple are thus referred to as radiation- or actinically curing orcurable systems.

Particularly advantageous properties can be obtained if the radiationcure is combined with a second crosslinking step so that it can becontrolled independently therefrom. Coating systems of this kind arereferred to as dual-cure systems (e.g. Macromol. Symp. 187, 531-542,2002, defined on p. 534).

Because of the environmental and economic requirements imposed on moderncoating systems, i.e., that they should use as little organic solventsas possible, or none at all, for adjusting the viscosity, there is adesire to use coatings raw materials which are already of low viscosity.Known for this purpose are polyisocyanates having allophanate groups asdescribed, inter alia, in EP-A 0 682 012.

In industry these substances are prepared by reacting a monohydric orpolyhydric alcohol with excess aliphatic and/or cycloaliphaticdiisocyanate (cf. GB-A 994 890, EP-A 0 000 194 or EP-A 0 712 840). Thisis followed by removal of unreacted diisocyanate by means ofdistillation under reduced pressure. According to DE-A 198 60 041 thisprocedure can also be carried out with OH-functional compounds havingactivated double bonds, such as hydroxyalkyl acrylates, althoughdifficulties occur in relation to the preparation of particularlylow-monomer products. Since the distillation step has to take place attemperatures up to 135° C., in order to be able to lower the residueisocyanate content sufficiently (<0.5% by weight of residual monomer),it is possible for double bonds to react, with polymerization, underthermal initiation, even during the purification process, meaning thatideal products are no longer obtained.

EP-A 0 825 211 describes a process for synthesizing allophanatestructures from oxadiazinetriones, although no radiation-curingderivatives with activated double bonds are known. All that is mentionedis the use of maleinate- and/or fumarate-containing polyesters; thepossibility of radiation curing is not described.

U.S. Pat. No. 5,777,024 describes the preparation of radiation-curingallophanates of low viscosity by a reaction of hydroxy-functionalmonomers that carry activated double bonds with allophanate-modifierisocyanurates that contain NCO groups.

The formation of allophanate compounds by ring opening of uretdioneswith alcohols is known in principle as a crosslinking mechanism inpowder coating materials (cf. Proceedings of the InternationalWaterborne, High-Solids, and Powder Coatings Symposium 2001, 28th,405-419, and also U.S.-A 2003/0153713). Nevertheless, the reactiontemperatures required for this purpose are too high (≧130° C.) for atargeted preparation of radiation-curing monomers based on allophanatewith activated double bonds.

Historically the direct reaction of uretdione rings with alcohols toallophanates was first investigated for solventborne, isocyanate-free,2K [2-component] polyurethane coating materials. Without catalysis thisreaction is of no technical importance, due to the low reaction rate (F.Schmitt, Angew. Makromol. Chem. (1989), 171, pp. 21-38). Withappropriate catalysts, however, the crosslinking reaction betweenHDI-based uretdione curatives and polyols is said to begin at 60 to 80°C. (K. B. Chandalia; R. A Englebach; S. L. Goldstein; R. W. Good; S. H.Harris; M. J. Morgan; P. J. Whitman; R. T. Wojcik, Proceedings of theInternational Waterborne, High-Solids, and Powder Coatings Symposium,(2001), pp. 77-89). The structure of these catalysts has not beenpublished to date. Commercial products prepared by utilizing thisreaction are also undisclosed to date.

In summary it may be stated that the preparation of radiation-curingallophanates of low viscosity having isocyanate-reactive groups by aring-opening reaction of alcohols that carry activated double bonds withuretdiones at temperatures ≦130° C. is not explicitly described by theprior art.

Surprisingly it has now been found that from the reaction of uretdioneswith olefinic unsaturated alcohols that preferably contain activateddouble bonds and saturated compounds having at least twoisocyanate-reactive groups it is possible, using ammonium salts orphosphonium salts of aliphatic carboxylic acids as catalysts, to obtainradiation-curing allophanates of low viscosity with low residual monomerfractions at temperatures even of ≦130° C. When such crosslinkerscontain not only radiation-curing functions but also functions that arereactive towards NCO groups, they are referred to as dual-curecrosslinkers.

SUMMARY OF THE INVENTIONN

The invention relates to a process for preparing binders whichcontain 1) allophanate groups, 2) groups that react with ethylenicallyunsaturated compounds with polymerization on exposure to actinicradiation (radiation-curing groups) and 3) optionally NCO-reactivegroups, by reacting at temperatures ≦130° C.

-   A) one or more NCO-functional compounds containing uretdione groups    with-   B) one or more compounds that contain isocyanate-reactive groups and    groups that react with ethylenically unsaturated compounds with    polymerization on exposure to actinic radiation (radiation-curing    groups), and then-   C) with one or more saturated, hydroxyl-containing compounds other    than B), at least one of these compounds having an OH functionality    of ≧2, in the presence of-   D) a catalyst containing one or more zinc compounds,    the reaction with compounds C) taking place at least proportionally    with the formation of allophanate groups.

The present invention also relates to the binders obtained by theprocess of the invention.

The present invention further relates to coating compositions comprising

-   a) one or more binders obtained in accordance with the invention,-   b) optionally one or more polyisocyanates containing free or blocked    isocyanate groups, which optionally contain groups which react with    ethylenically unsaturated compounds with polymerization on exposure    to actinic radiation,-   c) optionally compounds other than a), which contain groups which    react with ethylenically unsaturated compounds with polymerization    on exposure to actinic radiation, and optionally contain    NCO-reactive groups,-   d) optionally one or more isocyanate-reactive compounds containing    an active hydrogen which are free from groups which react with    ethylenically unsaturated compounds with polymerization on exposure    to actinic radiation, and-   e) one or more initiators.

DETAILED DESCRIPTION OF THE INVENTION

For the purposes of the present inventions the terms “radiation-curinggroups”, “actinically curing groups” and “groups that react withethylenically unsaturated compounds with polymerization on exposure toactinic radiation” are used synonymously.

The compounds of component B) include groups that react withethylenically unsaturated compounds with polymerization on exposure toactinic radiation, such as vinyl, vinyl ether, propenyl, allyl, maleyl,fumaryl, maleimide, dicyclopenta-dienyl, acrylamide, acryloyl andmethacryloyl groups. Preferred activated groups are vinyl ether,acrylate and/or methacrylate groups, more preferably acrylate groups.

NCO-reactive groups include OH-, SH- and NH-functional compounds,preferably hydroxyl groups, primary or secondary amino groups andaspartate groups, and more preferably hydroxyl groups.

Component A) includes any organic compounds which have at least oneuretdione and one NCO group. The compounds used in A) preferably have auretdione group content (calculated as C₂N₂O₂=84 g/mol) of from 3% to60%, more preferably from 10% to 50%, and most preferably from 25% to40% by weight.

The compounds used in A), in addition to having uretdione groups, alsopreferably have from 3% to 60%, more preferably from 10% to 50%, andmost preferably from 15% to 25% by weight of NCO groups (calculated asNCO=42 g/mol).

These compounds are preferably prepared by the catalytic dimerization ofaliphatic, cycloaliphatic, aromatic and/or araliphatic di- orpolyisocyanates using known processes (cf. J. Prakt. Chem. 1994, 336,page 196-198).

Suitable diisocyanates include 1,4-diisocyanatobutane,1,6-diisocyanatohexane, trimethylhexane diisocyanate, 1,3- and1,4-bis-isocyanatomethylcyclohexane, isophorone diisocyanate (IPDI),4,4′-diisocyanatodicyclohexyhnethane, 1,3- and 1,4-xylylene diisocyanate(XDI commercial product of Takeda, Japan), diphenylmethane4,4′-diisocyanate and diphenylmethane 2,4′-diisocyanate (MDI), 2,4- and2,6-toluene diisocyanate (TDI), or mixtures thereof. For the purposes ofthe invention it is preferred to use 1,6-diisocyanatohexane, isophoronediisocyanate or mixtures thereof.

Examples of catalysts employed for the dimerization reaction includetrialkylphosphines, dimethylaminopyridines andtris(dimethylamino)phosphine. The result of the dimerization reactiondepends in known manner on the catalyst used, on the process conditionsand on the diisocyanates employed. In particular it is possible forproducts to be formed which contain on average more than one uretdionegroup per molecule, the number of uretdione groups being subject to adistribution. Depending upon the catalyst used, the process conditionsand the diisocyanates employed, product mixtures are also formed whichin addition to uretdiones also contain other structural units, such asisocyanurate and/or iminooxadiazinedione.

Particularly preferred products may be obtained by the catalyticdimerization of HDI and have a free HDI content of less than 0.5% byweight; an NCO content of 17 to 25% by weight, preferably of 21 to 24%by weight; and a viscosity at 23° C. of from 20 to 500 mPas, preferablyfrom 50 to 200 mPas.

The generally NCO-functional compounds obtained by catalyticdimerization are preferably used directly as part of component A), butthey can also first be subjected to further reaction and then used ascomponent A). Further reactions include blocking the free NCO groups orfurther reaction of the NCO groups with NCO-reactive compounds having afunctionality of two or more to form iminooxadiazinedione, isocyanurate,urethane, allophanate, biuret urea, oxadiazinetrione, oxazolidinone,acylurea or carbodiimide groups. This results in compounds containinguretdione groups having a higher molecular weight, which, depending onthe chosen proportions, have different NCO contents.

Suitable blocking agents include alcohols, lactams, oximes, malonates,alkyl acetoacetates, triazoles, phenols, imidazoles, pyrazoles andamines, such as butanone oxime, diisopropylamine, 1,2,4-triazole,dimethyl-1,2,4-triazole, imidazole, diethyl malonate, ethylacetoacetate, acetone oxime, 3,5-dimethylpyrazole, ε-caprolactam,N-tert-butylbenzylamine, cyclopentanone carboxyethyl ester or mixturesof these blocking agents. The procedure for the blocking of NCO groupsis well known and described in Progress in Organic Coatings 1999, 36,148-172.

NCO-reactive compounds having a functionality of two or more forderivatizing the uretdiones used in A) can be the preceding di- and/orpolyisocyanates, and also simple alcohols with a functionality of two ormore, such as ethylene glycol, propane-1,2-diol, propane-1,3-diol,diethylene glycol, dipropylene glycol, the isomeric butanediols,neopentyl glycol, hexane-1,6-diol, 2-ethylhexanediol, tripropyleneglycol and the alkoxylated derivatives of these alcohols. Preferreddihydric alcohols are hexane-1,6-diol, dipropylene glycol andtripropylene glycol. Suitable trihydric alcohols include glycerol ortrimethylolpropane or their alkoxylated derivatives. Tetrahydricalcohols include pentaerythritol or its alkoxylated derivatives.

Additionally it is also possible to use compounds having a hydrophilicaction and containing at least one isocyanate-reactive group for thederivatization, individually or as a mixture. Compounds having ahydrophilic action are preferably used when the product of the inventionis to be dissolved or dispersed in water or aqueous mixtures.

Suitable compounds with a hydrophilic action include all ionic,potential ionic and nonionic hydrophilic compounds having at least oneisocyanate-reactive group. As isocyanate-reactive groups, thesecompounds preferably contain hydroxy and/or amino functions.

Ionic or potential ionic hydrophilic compounds are compounds which haveat least one isocyanate-reactive group and also at least onefunctionality, such as —COOY, —SO₃Y, —PO(OY)₂ (Y═H, NH₄ ⁺, metalcation), —NR₂, —NR₃ ⁺, —PR₃ ⁺ (R═H, alkyl, aryl). By potential ionichydrophilic groups are those compounds which on interaction with aqueousmedia enter into an optionally pH-dependent dissociation equilibrium andthus have a negative, positive or neutral charge.

Examples of suitable ionic compounds or compounds containing potentialionic groups are mono- and dihydroxycarboxylic acids, mono- anddiaminocarboxylic acids, mono- and dihydroxysulphonic acids, mono- anddiaminosulphonic acids, mono- and dihydroxyphosphonic acids or mono- anddiaminophosphonic acids and their salts. Examples include dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid,N-(2-aminoethyl)-β-alanine, 2-(2-aminoethylamino)-ethanesulphonic acid,ethylenediamine-propyl- or butylsulphonic acid, 1,2- or1,3-propylenediamine-β-ethylsulphonic acid, malic acid, citric acid,glycolic acid, lactic acid, glycine, alanine, taurine, lysine,3,5-diaminobenzoic acid, an adduct of IPDI and acrylic acid (EP-A 0 916647, Example 1) and its alkali metal and/or ammonium salts, the adductof sodium bisulphite with but-2-ene-1,4-diol, polyethersulphonate, thepropoxylated adduct of 2-butenediol and NaHSO₃ (described for example inDE-A 2 446 440, page 5-9, formula I-III) and also structural units whichcan be converted into cationic groups, such as N-methyldiethanolamine.

Preferred ionic or potential ionic compounds are those having carboxylor carboxylate, sulphonate groups and/or ammonium groups. Particularlypreferred ionic compounds are those which contain carboxyl and/orsulphonate groups as ionic or potential ionic groups, such as the saltsof N-(2-aminoethyl)-β-alanine, 2-(2-aminoethylamino)ethanesulphonicacid, the adduct of IPDI and acrylic acid (EP-A-0 916 647, Example 1)and also dimethylolpropionic acid.

As hydrophilic nonionic compounds it is possible to use compounds with apolyether structure, preferably alkylene oxide-based polyethers whichcontain at least one hydroxy or amino group as isocyanate-reactivegroup.

These compounds with a polyether structure include monofunctionalpolyalkylene oxide polyether alcohols containing on average 5 to 70,preferably 7 to 55, ethylene oxide units per molecule, with at least 30mol % of ethylene oxide, such as those obtained in known manner byalkoxylating suitable starter molecules (e.g. in Ullmanns Encyclopädieder technischen Chemie, 4th Edition, Vol. 19, Verlag Chemie, Weinheim,pp. 31-38).

Examples of suitable starter molecules include saturated monoalcoholssuch as methanol, ethanol, n-propanol, isopropanol, n-butanol,isobutanol, sec-butanol, the isomeric pentanols, hexanols, octanols andnonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol,n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols,hydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane,tetrahydrofurfuryl alcohol, diethylene glycol monoalkyl ethers such asdiethylene glycol monobutyl ether, unsaturated alcohols (such as allylalcohol, 1,1-dimethylallyl alcohol or oleyl alcohol), aromatic alcoholssuch as phenol, the isomeric cresols or methoxyphenols, araliphaticalcohols (such as benzyl alcohol, anisyl alcohol or cinnamyl alcohol),secondary monoamines (such as dimethylamine, diethylamine,dipropylamine, diisopropylamine, dibutylamine, bis(2-ethylhexyl)amine,N-methyl- and N-ethylcyclohexylamine or dicyclohexylamine) and alsoheterocyclic secondary amines (such as morpholine, pyrrolidine,piperidine or 1H-pyrazole). Preferred starter molecules are saturatedmonoalcohols. Particular preference is given to using diethylene glycolmonobutyl ether as the starter molecule.

Alkylene oxides suitable for the alkoxylation reaction are, inparticular, ethylene oxide and propylene oxide, which can be used in anyorder, separately from one another or in a mixture, in the alkoxylationreaction, so that block polyethers or copolyethers are obtained.

The compounds with a polyether structure are preferably purepolyethylene oxide polyethers or mixed polyalkylene oxide polyethers inwhich at least 30 mol %, preferably at least 40 mol %, of the alkyleneoxide units are ethylene oxide units. Preferred nonionic compounds aremonofunctional mixed polyalkylene oxide polyethers which contain atleast 40 mole % of ethylene oxide units and not more than 60 mole % ofpropylene oxide units.

Especially when using a hydrophilic agent containing ionic groups it isnecessary to examine its effect on the activity of the catalyst D). Forthis reason, if the hydrophilic polyisocyanates are to be used, nonionichydrophilic agents are preferred.

Examples of suitable compounds B), which can be used alone or inadmixture, include 2-hydroxyethyl (meth)acrylate, polyethylene oxidemono(meth)acrylate (e.g. PEA6/PEM6; Laporte Performance Chemicals Ltd.,UK), polypropylene oxide mono(meth)acrylate (e.g. PPA6, PPM5S; LaportePerformance Chemicals Ltd., UK), polyalkylene oxide mono(meth)acrylate(e.g. PEM63P, Laporte Performance Chemicals Ltd., UK),poly(ε-caprolactone) mono(meth)acrylates (e.g. Tone M100® Dow,Schwalbach, DE), 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, hydroxybutyl vinyl ether, 3-hydroxy-2,2-dimethylpropyl(meth)acrylate, the hydroxy-functional mono-, di- or higher functionalacrylates such as glyceryl di(meth)acrylate, trimethylolpropanedi(meth)acrylate, pentaerythritol tri(meth)acrylate or dipentaerythritolpenta(meth)acrylate, which are obtained by reacting polyhydric,optionally alkoxylated, alcohols such as trimethylolpropane, glycerol,pentaerythritol or dipentaerythritol with (meth)acrylic acid.

Also suitable as component B) are alcohols obtained from the reaction ofacids containing double bonds with epoxide compounds optionallycontaining double bonds, such as the reaction products of (meth)acrylicacid with glycidyl (meth)acrylate or bisphenol A diglycidyl ether.Additionally, it is also possible to use unsaturated alcohols which areobtained from the reaction of optionally unsaturated acid anhydrideswith hydroxy compounds and epoxide compounds that optionally containacrylate groups. Examples include the reaction products of maleicanhydride with 2-hydroxyethyl (meth)acrylate and glycidyl(meth)acrylate.

Particularly preferred compounds of component B) are 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, Tone M100®(Dow, Schwalbach, DE), polyethylene oxide mono(meth)acrylate (e.g.PEA6/PEM6; Laporte Performance Chemicals Ltd., UK), polypropylene oxidemono(meth)acrylate (e.g. PPA6, PPM5S; Laporte Performance ChemicalsLtd., UK) and the reaction products of acrylic acid with glycidylmethacrylate.

Component C) is selected from one or more saturated hydroxyl-containingcompounds other than B), at least one of these compounds having an OHfunctionality of ≧2. The compounds may be monomeric and/or polymeric.

Suitable compounds are low molecular weight mono-, di- or polyols suchas short-chain, i.e., containing 2 to 20 carbon atoms, aliphatic,araliphatic or cycloaliphatic monoalcohols, diols or polyols. Examplesof monoalcohols include methanol, ethanol, the isomeric propanols,butanols, pentanols, and also diacetone alcohols, fatty alcohols orfluorinated alcohols (such as those obtained under the name Zonyl® fromDuPont.

Examples of diols include ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, dipropylene glycol,tripropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,neopentyl glycol, 2-ethyl-2-butylpropanediol, trimethylpentanediol,positionally isomeric diethyloctanediols, 1,3-butylene-glycol,cyclohexanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, 1,2- and1,4-cyclohexanediol, hydrogenated bisphenol A(2,2-bis(4-hydroxy-cyclohexyl)propane), and 2,2-dimethyl-3-hydroxypropyl2,2-dimethyl-3-hydroxypropionate. Examples of suitable triols includetrimethylolethane, trimethylolpropane or glycerol and examples ofsuitable polyols include ditrimethylolpropane, pentaerythritol,dipentaerythritol and orbitol. Preferred alcohols are 1,4-butanediol,1,4-cyclohexanedimethanol, 1,6-hexanediol and trimethylolpropane.

Suitable higher molecular weight polyols include polyester polyols,polyether polyols, hydroxy-functional (meth)acrylate (co)polymers,hydroxy-functional polyurethanes or the corresponding hybrids (cf. RömppLexikon Chemie, pp. 465-466, 10th ed. 1998, Georg-Thieme-Verlag,Stuttgart).

For the preparation of the hydroxy-functional polyesters there are 6groups of monomer constituents in particular that may be employed.

-   1. (Cyclo)alkanediols such as dihydric alcohols having    (cyclo)aliphatically bound hydroxyl groups. Examples include the    preceding low molecular weight diols, and also polyethylene,    polypropylene or polybutylene glycols having a number average    molecular weight of 200 to 4000, preferably 300 to 2000 and more    preferably 450 to 1200. Reaction products of these diols with    ε-caprolactone or other lactones are also suitable diols.-   2. Alcohols with a functionality of 3 or more and having a molecular    weight of 92 to 254, such as glycerol, trimethylolpropane,    pentaerythritol, dipentaerythritol and sorbitol; polyethers prepared    starting from these alcohols, such as the reaction product of 1 mol    of trimethylolpropane with 4 mol of ethylene oxide; or alcohols    obtained by the reaction of these alcohols with ε-caprolactone or    other lactones.-   3. Monoalcohols such as ethanol, 1- and 2-propanol, 1- and    2-butanol, 1-hexanol, 2-ethylhexanol, cyclohexanol and benzyl    alcohol.-   4. Dicarboxylic acids having a number average molecular weight of    104 to 600 and/or their anhydrides, such as phthalic acid, phthalic    anhydride, isophthalic acid, tetrahydrophthalic acid,    tetra-hydrophthalic anhydride, hexahydrophthalic acid,    hexahydrophthalic anhydride, cyclohexanedicarboxylic acid, maleic    anhydride, fumaric acid, malonic acid, succinic acid, succinic    anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid,    sebacic acid, dodecanedioic acid, and hydrogenated dimer fatty    acids.-   5. Higher polyfunctional carboxylic acids and/or their anhydrides    such as trimellitic acid and trimellitic anhydride.-   6. Monocarboxylic acids, such as benzoic acid, cyclohexanecarboxylic    acid, 2-ethylhexanoic acid, caproic acid, caprylic acid, capric    acid, lauric acid, and natural and synthetic fatty acids.

Suitable hydroxyl-containing polyesters include the reaction product ofat least one constituent from group 1 or 2 with at least one constituentfrom group 4 or 5. It is also possible to use the previously describedreaction products of alcohols with lactones. The hydroxyl-containingpolyesters have number-average molecular weights of 500 to 10,000,preferably 800 to 3000 g/mol and a hydroxyl group content of 1% to 20%,preferably 3% to 15% by weight. The polyesters can be employed at 100%solids or in solution in the solvents or reactive diluents that aredescribed below and are suitable for the process of the invention.

In addition to the preceding polyester polyols, dendrimeric orhyperbranched compounds are also suitable, such as those obtained fromethoxylated pentaerythritol and dimethylolpropionic acid.

Suitable polycarbonate polyols are obtained by reacting the alcoholsmentioned above for preparing the polyester polyols with organiccarbonates such as diphenyl, dimethyl or diethyl carbonate in accordancewith known methods. They preferably have number average molecularweights of 500 to 5000, more preferably 750 to 2500 g/mol, and hydroxylfunctionalities of 1.5 to 3.

Examples of suitable polyethers include the alkylene oxide polyethersthat are prepared from the previously mentioned low molecular weightmono-, di- or polyols. Also suitable are polyethers obtained bypolymerizing tetrahydrofuran. The polyethers have number averagemolecular weights of 400 to 13,000, preferably 400 to 2500, and morepreferably 500 to 1200 g/mol, and a hydroxyl group content of 1% to 25%,preferably 3% to 15% by weight.

(Meth)acrylate (co)polymers are described at length in WO 03/000812 onpages 8 to 16 as well as suitable preparation processes, the(meth)acrylate (co)polymers that are suitable in accordance with theinvention are those which have at least one hydroxyl group. The(meth)acrylate (co)polymers preferably have number average molecularweights of 500 to 10,000, more preferably 1000 to 5000, and a hydroxylgroup content of 1% to 20%, preferably 3% to 15% by weight.

Particular preference is given to monomeric di- or triols, and alsopolyethers and/or polylactones derived therefrom and having a nnumberaverage molecular weight below 1000 g/mol.

Suitable catalyst compounds D) include, in addition to the zinccompounds for use in accordance with the invention, the compounds knownfor catalyzing the reaction of isocyanate groups withisocyanate-reactive groups, individually or in mixtures with oneanother.

Examples include tertiary amines such as triethylamine, pyridine,methylpyridine, benzyldimethylamine, N,N-endoethylenepiperazine,N-methylpiperidine, penta-methyldiethylenetriamine,N,N-dimethylaminocyclohexane, N,N′-dimethylpiperazine or1,4-diazabicyclo[2.2.2]octane (DABCO), or metal salts such as iron(III)chloride, tin(II) octoate, tin(II) ethylcaproate, tin(II) palmitate,dibutyltin(IV) dilaurate, dibutyltin(IV) diacetate and molybdenumglycolate or mixtures of such catalysts.

Suitable zinc compounds include any organic or inorganic zinc compounds,such as zinc oxide, zinc sulphide, zinc carbonate, zinc fluoride, zincchloride, zinc bromide, zinc iodide, zinc phosphate, zinc borate, zinctitanate, zinc hexafluorosilicate, zinc sulphite, zinc sulphate, zincnitrate, zinc tetrafluoroborate, zinc acetate, zinc octoate, zinccyclohexanebutyrate, zinc laurate, zinc palmitate, zinc stearate, zincbeherate, zinc citrate, zinc gluconate, zinc acetylacetonate, zinc2,2,6,6-tetramethyl-3,5-heptanedionate, zinc trifluoracetate, zinctrifluoromethane-sulphonate, zinc dimethyldithiocarbamate and mixturesof these compounds.

Preferred catalysts D) are zinc octoate and/or zinc acetylacetonate.Preferably, zinc compounds are exclusively used as catalysts D).

It is also possible to bring the catalysts D) by methods known to theskilled worker onto support materials and to use them as heterogeneouscatalysts.

The compounds of catalyst component D) can be dissolved advantageouslyin one of the components used in the process, or in a portion thereof.In particular, the zinc compounds for use in accordance with theinvention dissolve very well in the polar hydroxyalkyl acrylates, sothat D) in solution in small amounts of B) can be metered in as aconcentrated solution in liquid form.

In the process of the invention catalyst component D) is preferably usedin amounts of 0.001 to 5.0% by weight, more preferably 0.01 to 2.0% byweight and most preferably 0.05 to 1.0% by weight, based on solidscontent of the product.

As component E) it is possible to use solvents or reactive diluents.Suitable solvents are inert towards the functional groups present in theproduct from the time of their addition until the end of the process.Suitable solvents include those used in the coating industry, such ashydrocarbons, ketones and esters, e.g. toluene, xylene, isooctane,acetone, butanone, methyl isobutyl ketone, ethyl acetate, butyl acetate,tetrahydrofuran, N-methylpyrrolidone, dimethylacetamide anddimethylformamide. It is preferred not to add any solvent.

As reactive diluents it is possible to use compounds which during UVcuring are (co)polymerized and thus incorporated into the polymernetwork. When these reactive diluents are contacted with NCO-containingcompounds A), they must be inert towards NCO groups. When they are addedonly after the reaction of A) with B), this restriction does not apply.Such reactive diluents are described, by way of example, in P. K. T.Oldring (Ed.), Chemistry & Technology of UV & EB Formulations ForCoatings, Inks & Paints, Vol. 2, 1991, SITA Technology, London, pp.237-285. They may be esters of acrylic acid or methacrylic acid,preferably acrylic acid, with mono- or polyfunctional alcohols. Examplesof suitable alcohols include the isomeric butanols, pentanols, hexanols,heptanols, octanols, nonanols and decanols; cycloaliphatic alcohols suchas isobornol, cyclohexanol and alkylated cyclohexanols; dicyclopentanol;arylaliphatic alcohols such as phenoxyethanol and nonylphenylethanol;and tetrahydrofurfuryl alcohols. Additionally, it is possible to usealkoxylated derivatives of these alcohols.

Suitable dihydric alcohols include alcohols such as ethylene glycol,propane-1,2-diol, propane-1,3-diol, diethylene glycol, dipropyleneglycol, the isomeric butanediols, neopentyl glycol, hexane-1,6-diol,2-ethylhexanediol, tripropylene glycol or alkoxylated derivatives ofthese alcohols. Preferred dihydric alcohols are hexane-1,6-diol,dipropylene glycol and tripropylene glycol. Suitable trihydric alcoholsinclude glycerol or trimethylolpropane or their alkoxylated derivatives.Tetrahydric alcohols include pentaerythritol or its alkoxylatedderivatives.

The binders of the invention must be stabilized against prematurepolymerization. Therefore, as a constituent of component E), beforeand/or during the reaction, preferably phenolic stabilizers are addedwhich inhibit the polymerization. Use is made in this context of phenolssuch as para-methoxyphenyl, 2,5-di-tert-butylhydroquinone or2,6-di-tert-butyl-4-methylphenol. Also suitable are N-oxyl compounds forstabilization, such as 2,2,6,6-tetramethylpiperidine N-oxide (TEMPO) orits derivatives. The stabilizers can also be incorporated chemicallyinto the binder; suitability in this context is possessed by compoundsof the abovementioned classes, especially if they still carry furtherfree aliphatic alcohol groups or primary or secondary amine groups andthus can be attached chemically to compounds of component A) by way ofurethane or urea groups. Particularly suitable for this purpose are2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide. Preferred are phenolicstabilizers, especially para-methoxyphenol and/or2,6-di-tert-butyl-4-methylphenol.

Other stabilizers, such as hindered amine light stabilizers (HALS), incontrast, are used less preferably in E), since they are known not toenable such effective stabilization and instead may lead to “creeping”free-radical polymerization of unsaturated groups.

In order to stabilize the reaction mixture, in particular theunsaturated groups, against premature polymerization it is possible topass an oxygen-containing gas, preferably air, into and/or over thereaction mixture. It is preferred for the gas to have a very lowmoisture content in order to prevent unwanted reaction in the presenceof isocyanate.

In general a stabilizer is added during the preparation of the bindersof the invention, and at the end, in order to achieve a long-termstability, stabilization is repeated with a phenolic stabilizer, andoptionally the reaction product is saturated with air.

In the process of the invention the stabilizer component is typicallyused in amounts of 0.001 to 5.0% by weight, preferably 0.01 to 2.0% byweight and more preferably 0.05 to 1.0% by weight, based on the solidscontent of the product.

The process of the invention is carried out is such that A) is firstreacted with B) until all of the NCO groups have been reacted. Theresulting intermediate can optionally be stored and/or transported. Thisis then followed by the reaction of the uretdione groups with componentC).

The ratio of NCO groups in A) to NCO-reactive groups in B) is from 1:1to 1:1.5, preferably 1:1 to 1:1.2 and more preferably 1:1. The ratio ofuretdione groups in A) to hydroxyl groups in C) is 1:0.4 to 1:6,preferably 1:0.9 to 1:4 and more preferably 1:0.9 to 1:2. In addition itis essential that the sum of the NCO groups and uretdione groups in A)exceeds the sum of the NCO-reactive groups and uretdione-reactive groupsin B).

Depending upon the proportions selected, products are obtained whicheither are free from hydroxyl groups or still contain hydroxyl groups.These products preferably contain not only the radiation-curing groupsbut also NCO-reactive groups. The process of the invention is carriedout preferably at temperatures of 20 to 130° C., more preferably of 40to 90° C.

The viscosity of the binders obtained in accordance with the inventiondepends in particular on functionality, molecular weight and thechemical nature of component C) and also on the stoichiometricproportions used. When the preferred monomeric diols or triols, and alsopolyethers and/or polyacetones derived therefrom having a number averagemolecular weight below 1000 g/mol are used, this results in binderspreferably having a viscosity of below 100,000 mPa·s at 23° C., morepreferably below 75,000 mPa·s at 23° C. The number average molecularweight is preferably 500 to 5000, more preferably 800 and 2000 g/mol.

The process of the invention may be carried out continuously, e.g., in astatic mixer, or batchwise, e.g., in a stirred reactor.

Preferably the process of the invention is carried out in a stirredreactor, in which case the sequence of addition of components A) and B)in the first process step and of intermediate AB) and component C) inthe second process step is arbitrary. The stabilizers present in E) areadded preferably before component B) is exposed to a thermal load. Theother parts of component E) can be added at any desired time. The zinccompounds of D) are preferably not added until after the preparation ofthe intermediate AB).

The course of the reaction can be monitored by means of suitablemeasuring instruments installed in the reaction vessel and/or on thebasis of analyses of samples taken. Suitable techniques are known. Theyinclude, for example, viscosity measurements, measurements of therefractive index, of the OH content, gas chromatography (GC), nuclearmagnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy andnear-infrared (NIR) spectroscopy. Preferred is using IR to check for anyfree NCO groups present (for aliphatic NCO groups, band at approximatelyν=2272 cm⁻¹) and, in particular, for uretdione groups (e.g. band foruretdiones based on hexamethylene diisocyanate at ν=1 761 cm⁻¹) and toGC analyses for unreacted compounds from B) and C).

It is possible not to carry out the reaction of the uretdione groupswith the hydroxyl groups completely, but instead to terminate thereaction on reaching a certain conversion. A further (creeping) reactioncan then be suppressed by adding known acidic agents for stabilizingisocyanate groups. Preferred acids or acid derivatives include benzoylchloride, phthaloyl chloride, phosphinous, phosphonous and/orphosphorous acid, phosphinic, phosphonic and/or phosphoric acid, theacidic esters of the preceding 6 acid types, sulphuric acid and itsacidic esters and/or sulphonic acids.

The binders of the invention can be used for producing coatings andpaints and also adhesives, printing inks, casting resins, dentalcompounds, sizes, photoresists, stereolithography systems, resins forcomposite materials and sealants. In the case of adhesive bonding orsealing, it is a requirement, in the case of UV radiation curing, atleast one of the two substrates to be bonded or sealed to one another ispermeable to UV radiation, i.e, it must be transparent. In the case ofelectron beams, sufficient permeability for electrons should be ensured.Preferably, the binders are used in paints and coatings.

The coating compositions according to the invention contain

-   a) one or more binders obtained in accordance with the invention,-   b) optionally one or more polyisocyanates containing free or blocked    isocyanate groups, which optionally contain groups which react with    ethylenically unsaturated compounds with polymerization on exposure    to actinic radiation,-   c) optionally compounds other than a), which contain groups which    react with ethylenically unsaturated compounds with polymerization    on exposure to actinic radiation, and optionally contain    NCO-reactive groups,-   d) optionally one or more isocyanate-reactive compounds containing    an active hydrogen which are free from groups which react with    ethylenically unsaturated compounds with polymerization on exposure    to actinic radiation,-   e) one or more initiators and-   f) optionally additives.

Suitable polyisocyanates b) are aromatic, araliphatic, aliphatic orcycloaliphatic di- or polyisocyanates. Mixtures of such diisocyanates orpolyisocyanates can also be used. Examples of suitable diisocyanates orpolyisocyanates include butylene diisocyanate, hexamethylenediisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4- and/or2,4,4-trimethylhexamethylene diisocyanate, the isomericbis(4,4′-isocyanatocyclohexyl)methanes or mixtures thereof of anydesired isomer content, isocyanatomethyl-1,8-octane diisocyanate,1,4-cyclohexylene diisocyanate, the isomeric cyclohexanedimethylenediisocyanates, 1,4-phenylene diisocyanate, 2,4- and/or 2,6-tolylenediisocyanate, 1,5-naphthylene diisocyanate, 2,4′- or4,4′-diphenylmethane diisocyanate, triphenylmethane4,4′,4″-triisocyanate or polyisocyanate adducts prepared these di- andpolyisocyanates and containing urethane, urea, carbodiimide, acylurea,isocyanurate, allophanate, biuret, oxadiazinetrione, uretdione,iminooxadiazine dione groups, and mixtures thereof.

Preferred are polyisocyanate adducts based on oligomerized and/orderivatized diisocyanates which have been freed from excess diisocyanateby suitable methods, particularly those adducts prepared fromhexamethylene diisocyanate, isophorone diisocyanate and of the isomericbis(4,4′-isocyanatocyclohexyl)-methanes and also mixtures thereof.Especially preferred are polyisocyanate adducts containing isocyanurateand/or iminooxadiazine dione groups and prepared from HDI and also topolyisocyanate adducts containing isocyanurate groups and prepared fromIPDI.

It is also possible to use the preceding isocyanates blocked with knownblocking agents. Examples include alcohols, lactams, oximes, malonates,alkyl acetoacetates, triazoles, phenols, imidazoles, pyrazoles and alsoamines, such as butanone oxime, diisopropylamine, 1,2,4-triazole,dimethyl-1,2,4-triazole, imidazole, diethyl malonate, ethylacetoacetate, acetone oxime, 3,5-dimethylpyrazole, ε-caprolactam,N-tert-butyl-benzylamine, cyclopentanone carboxyethyl ester and mixturesthereof.

Polyisocyanates b) may optionally contain one or more functional groupswhich react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation. These groups may be preparedby reacting the unsaturated and isocyanate-reactive compounds specifiedunder B), including the preferred ranges, with saturated polyisocyanatesby known methods. NCO-containing urethane acrylates of this kind areavailable commercially from Bayer AG, Leverkusen, DE as Roskydal® UA VPLS 2337, Roskydal® UA VP LS 2396 or Roskydal® UA XP 2510.

Suitable compounds for use as component c) are polymers (such aspolyacrylates, polyurethanes, polysiloxanes, polyesters, polycarbonatesand polyethers) containing groups which react, with polymerization, withethylenically unsaturated compounds through exposure to actinicradiation. Such groups include α,β-unsaturated carboxylic acidderivatives such as acrylates, methacrylates, maleates, fumarates,maleimides and acrylamides; vinyl ethers; propenyl ethers; allyl ethers;and compounds containing dicyclopentadienyl units. Preferred areacrylates and methacrylates. Examples include the reactive diluentsknown in radiation curing technology and described as suitable for useunder E) (cf. Römpp Lexikon Chemie, p. 491, 10th ed. 1998,Georg-Thieme-Verlag, Stuttgart) or the known binders from radiationcuring technology, such as polyether acrylates, polyester acrylates,urethane acrylates, epoxy acrylates, melamine acrylates, siliconeacrylates, polycarbonate acrylates and acrylated polyacrylates, whichoptionally contain isocyanate-reactive groups, preferably hydroxylgroups.

Suitable compounds d) include the hydroxy-functional monomeric orpolymeric compounds described under C), and also water, which iscontacted with the remaining constituents only after coating, optionallyin the form of atmospheric moisture. Additionally it is possible to useNH-functional compounds such as amine-terminated polyethers, polyaminesand aspartates.

Suitable initiators for free-radical polymerization, which can be usedas component e), are those which can be activated thermally and/or byradiation. Photoinitiators, which are activated by UV or visible light,are preferred in this context. The photoinitiators are known compounds.A distinction is made between unimolecular (type I) and bimolecular(type II) initiators. Suitable (type I) systems include aromatic ketonecompounds, e.g. benzophenones in combination with tertiary amines,alkylbenzophenones, 4,4′-bis(dimethylamino)benzophenone (Michler'sketone), anthrone and halogenated benzophenones or mixtures thereof.Suitable (type II) initiators include benzoin and its derivatives,benzil ketals, acylphosphine oxides,2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylphosphine oxides,phenylglyoxylic esters, camphorquinone, α-aminoalkylphenones,α,α-dialkoxyacetophenones and α-hydroxyalkylphenones.

The initiators are used in amounts of 0.1% to 10% by weight, preferably0.1% to 5% by weight, based on the weight of the film-forming binder.The initiators can be used individually or, to obtain advantageoussynergistic effects, in combination with one another.

When electron beams are used instead of UV irradiation there is no needfor a photoinitiator. Electron beams are generated by means of thermalemission and accelerated by way of a potential difference. Thehigh-energy electrons then pass through a titanium foil and are guidedonto the binders to be cured. The general principles of electron beamcuring are described in detail in “Chemistry & Technology of UV & EBFormulations for Coatings, Inks & Paints”, Vol. 1, P. K. T Oldring(Ed.), SITA Technology, London, England, pp. 101-157, 1991.

Thermal curing of the activated double bonds can take place with theaddition of thermally decomposing free-radical initiators. Suitableinitiators include peroxy compounds such as dialkoxy dicarbonates, forexample, bis(4-tert-butylcyclohexyl) peroxydicarbonate; dialkylperoxides such as dilauryl peroxide; peresters of aromatic or aliphaticacids such as tert-butyl perbenzoate or tert-amyl peroxy2-ethylhexanoate; inorganic peroxides such as ammonium peroxodisulphateor potassium peroxodisulphate; organic peroxides such as2,2-bis(tert-butylperoxy)butane, dicumyl peroxide or tert-butylhydroperoxide; and azo compounds such as2,2′-azobis[N-(2-propenyl)-2-methylpropionamides],1-[(cyano-1-methylethyl)azo]formamides,2,2′-azobis(N-butyl-2-methylpropionamides),2,2′-azobis(N-cyclohexyl-2-methylpropionamides), 2,2′-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamides}, 2,2′-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamides, or 2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl] propionamides. Alsosuitable are highly substituted 1,2-diphenylethanes (benzpinacols) suchas 3,4-dimethyl-3,4-diphenylhexane, 1,1,2,2-tetraphenylethane-1,2-diolor the silylated derivatives thereof.

It is also possible to use a combination of initiators activable by UVlight and thermally.

Additives f) include solvents of the type specified above under E).Additionally, it is possible for f), in order to increase the weatherstability of the cured coating film, to contain UV absorbers and/or HALSstabilizers. Preferred is a combination of these stabilizers. The UVabsorbers should have an absorption range of not more than 390 nm, suchas the triphenyltriazine types (e.g. Tinuvin® 400 (CibaSpezialitätenchemie GmbH, Lampertheim, DE)), benzotriazoles such asTinuvin® 622 (Ciba Spezialitätenchemie GmbH, Lampertheim, DE) or oxalicdianilides (e.g. Sanduvor® 3206 (Clariant, Muttenz, CH))). They areadded at 0.5% to 3.5% by weight, based on resin solids. Suitable HALSstabilizers are also available commercially and include (Tinuvin® 292 orTinuvin® 123 (Ciba Spezialitätenchemie GmbH, Lampertheim, DE) orSanduvor® 3258 (Clariant, Muttenz, CH). They are preferably added inamounts of 0.5% to 2.5% by weight based on resin solids.

It is also possible for component f) to contain pigments, dyes, fillers,levelling additives and devolatilizing additives.

Additionally it is possible, if necessary, for the catalysts known frompolyurethane chemistry for accelerating the NCO/OH reaction to bepresent in f). They include tin salts or zinc salts or organotincompounds, tin soaps and/or zinc soaps, such as tin octoate, dibutyltindilaurate, dibutyltin oxide, tertiary amines such asdiazabicyclo[2.2.2]octane (DABCO), bismuth compounds, zirconiumcompounds or molybdenum compounds.

The application of the coating compositions of the invention to thematerial to be coated takes place using the methods known in coatingstechnology, such as spraying, knife coating, rolling, pouring, dipping,spin coating, brushing or squirting or by means of printing techniquessuch as screen, gravure, flexographic or offset printing and also bymeans of transfer methods.

Suitable substrates include wood, metal, including in particular metalas used in the applications of wire enamelling, coil coating, cancoating or container coating, and also plastic, including plastic in theform of films, especially ABS, AMMA, ASA, CA, CAB, EP, UF, CF, MF, MPF,PF, PAN, PA, PE, HDPE, LDPE, LLDPE, UHMWPE, PET, PMMA, PP, PS, SB, PUR,PVC, RF, SAN, PBT, PPE, POM, PUR-RIM, SMC, BMC, PP-EPDM, and UP(abbreviations according to DIN 7728T1), paper, leather, textiles, felt,glass, wood, wood materials, cork, inorganically bonded substrates suchas wooden boards and fiber cement slabs, electronic assemblies ormineral substrates. It is also possible to coat substrates containing avariety of the preceding materials, or to coat already coated substratessuch as vehicles, aircraft or boats and also parts thereof, especiallyvehicle bodies or parts for exterior mounting. It is also possible toapply the coating compositions to a substrate temporarily, then to curethem partly or fully and optionally to detach them again, in order toproduce films.

For curing it is possible to remove solvents present entirely or partlyby flashing off. Subsequently or simultaneously it is possible for theoptional thermal and the photochemical curing operation or operations tobe carried out in succession or simultaneously. If necessary the thermalcuring can take place at room temperature or at elevated temperature,preferably at 40 to 160° C., preferably at 60 to 130° C. and morepreferably at 80 to 110° C.

Where photoinitiators are used in e) the radiation cure takes placepreferably by exposure to high-energy radiation, in other words UVradiation or daylight, such as light having a wavelength 200 to 700 nm.Radiation sources of light or UV light include high-pressure ormedium-pressure mercury vapor lamps. It is possible for the mercuryvapor to have been modified by doping with other elements such asgallium or iron. Lasers, pulsed lamps (known under the designation of UVflashlight lamps), halogen lamps or excimer emitters may also be used.As an inherent part of their design or through the use of specialfilters and/or reflectors, the emitters may be equipped so that part ofthe UV spectrum is prevented from being emitted. By way of example, forreasons of occupational hygiene, for example, the radiation assigned toUV-C or to UV-C and UV-B may be filtered out. The emitters may beinstalled in stationary fashion, so that the material for irradiation isconveyed past the radiation source by means of a mechanical device, orthe emitters may be mobile and the material for irradiation may remainstationary during curing. The radiation dose which is normallysufficient for crosslinking in the case of UV curing is from 80 to 5000mJ/cm².

Irradiation can also be carried out in the absence of oxygen, such asunder an inert gas atmosphere or an oxygen-reduced atmosphere. Suitableinert gases are preferably nitrogen, carbon dioxide, noble gases orcombustion gases. Irradiation may additionally take place by coveringthe coating with media transparent to the radiation. Examples includepolymeric films, glass or liquids such as water.

Depending on the radiation dose and curing conditions it is possible tovary the type and concentration of any initiator used in known manner.

Particular preference is given to carrying out curing usinghigh-pressure mercury lamps in stationary installations. Photoinitiatorsare then employed at concentrations of from 0.1% to 10% by weight, morepreferably from 0.2% to 3.0% by weight, based on the solids content ofthe coating composition. For curing these coatings it is preferred touse a dose of from 200 to 3000 mJ/cm², measured in the wavelength rangefrom 200 to 600 nm.

When thermally activable initiators are used in d), curing is carriedout by increasing the temperature. The thermal energy may be introducedinto the coating by means of radiation, thermal conduction and/orconvection using ovens, near-infrared lamps and/or infrared lamps thatare known in coatings technology.

The applied film thicknesses (prior to curing) are typically between 0.5and 5000 μm, preferably between 5 and 1000 μm and more preferablybetween 15 and 200 μm. Where solvents are used, they are removed afterapplication and before curing by known methods.

EXAMPLES

All percentages are by weight unless indicated otherwise.

The determination of the NCO contents in % was determined byback-titration with 0.1 mol/l hydrochloric acid following reaction withbutylamine in accordance with DIN EN ISO 11909.

The viscosity measurements were carried out with a cone-plateviscosimeter (SM-KP), Viskolab LC3/ISO from Paar Physica, Ostfildern, DEin accordance with ISO/DIS 3219:1990.

Infrared spectroscopy was on liquid films applied between sodiumchloride plates on a model 157 instrument from Perkin Elmer, Überlingen,DE.

The amount of residue monomers and amount of volatile synthesiscomponents were analyzed by means of GC (method using tetradecane asinternal standard, oven temperature 110° C., injector temperature 150°C., carrier gas helium, instrument: 6890 N, Agilent, Waldbronn, DE,column: Restek RT 50, 30 m, 0.32 mm internal diameter, film thickness0.25 μm).

The solids content was determined in accordance with DIN 53216/1 draft4/89, ISO 3251.

An ambient temperature of 23° C., which prevailed at the time when theexperiments were conducted is referred to as RT.

-   Desmodur® N 3400—HDI polyisocyanate predominantly containing    uretdione groups, viscosity 185 mPas/23° C., NCO content 21.4%,    commercial product of Bayer MaterialScience AG, Leverkusen, DE-   Desmorapid® Z—dibutyltin dilaurate (DBTL), commercial product of    Bayer MaterialScience AG, Leverkusen, DE-   Darocur® 1173—photoinitiator, commercial product of Ciba    Spezialitätenchemie GmbH, Lampertheim, DE

Example 1 describes the preparation of a urethane acrylate containinguretdione groups by urethanization, and this acrylate is used inExamples 2-4.

Example 1 Urethane Acrylate Containing Uretdione Groups

A three-neck flask with reflux condenser, stirrer, dropping funnel andair passage (0.5 l/h) was initially charged at RT with 194.90 g ofDesmodur® N3400, 0.31 g of 2,6-di-tert-butyl-4-methylphenol and 0.005 gof Desmorapid® Z and this initial charge was then heated to 60° C.116.00 g of 2-hydroxyethyl acrylate was slowly added dropwise, duringwhich a maximum temperature of 70° C. was attained. Thereafter thereaction mixture was held at 70° C. until the NCO content was <0.1%.During cooling, the product solidified to a waxy solid.

Example 2 Inventive Allophanate-Containing Binder

In an apparatus similar to that used in Example 1, 175.35 g of theurethane acrylate from Example 1 were melted at 80° C. and 50.0 g ofbutyl acetate, 24.1 g of a polyether with an average of 4-foldethoxylation, prepared starting from trimethylolpropane (hydroxyl number550, dynamic viscosity 505 mPa·s at 23° C.) and 0.64 g of zinc(II)acetylacetonate were added. The reaction mixture was stirred at 80° C.until after 14.0 h only a very weak signal for uretdione groups wasdetected in the IR spectrum at ν=1768 cm⁻¹. The resulting clear producthad a viscosity of 3100 mPa·s/23° C., a solids content of 81.1% and anNCO content of 0%.

Example 3 Inventive Allophanate-Containing Binder

Example 2 was repeated with the difference that 167.13 g of the urethaneacrylate and 32.04 g of the polyether were used. The reaction mixturewas stirred at 80° C. until after 2 h only a very weak signal foruretdione groups was detected in the IR spectrum at ν=1768 cm⁻¹.Thereafter 0.20 g of isophthal dichloride was stirred in and thereaction mixture was cooled to RT. The resulting clear product had aviscosity of 1870 mPa·s/23° C., a solids content of 80.2%, a hydroxylnumber of 32 (theoretical: 35) and an NCO content of 0%.

Example 4 Inventive Allophanate-Containing Binder

Example 2 was repeated with the difference that only 66.8 g of theurethane acrylate, 12.8 g of the polyether, 20.0 g of butyl acetate and0.34 g of zinc(II)ethylhexanoate were used. The reaction mixture wasstirred at 80° C. until after 8.5 h only a very weak signal foruretdione groups was detected in the IR spectrum at ν=1768 cm⁻¹.Thereafter 0.08 g of isophthal dichloride was stirred in and thereaction mixture was cooled to RT. The resulting clear product had aviscosity of 1730 mPa·s/23° C., a solids content of 80.8%, a hydroxylnumber of 37 (theoretical: 35) and an NCO content of 0%.

Comparison Examples 5 and 6 Attempts to Prepare anAllophanate-Containing

Binder The catalysts described in U.S.-A 2003/0153713 for thecrosslinking of powder coating compositions containing uretdionegroup-containing curing agents and polymeric hydroxyl compounds withoutactivated double bonds were examined for suitability.

Comparison Example 5-Example 3 was repeated with the difference that thecatalyst from Example 1 was replaced with an equal molar amount oftetrabutylammonium hydroxide.

Comparsion Example 6-Example 3 was repeated with the difference that thecatalyst from Example 1 was replaced with an equal molar amount oftetrabutylammonium fluoride. (Comparison) Example 2 5 6 Reaction timeafter addition 3.0 h 2.5 h 2.0 h of catalyst Visual assessment ClearVery cloudy Very cloudy Solids content [%] 81.1 81.7 82.2 Viscosity [mPas] at 23° C. 5,000 12,000 16,000

The comparison shows that the products according to the comparisonExamples 5 and 6 have higher viscosities and because of the significantcloudiness that occurs, are virtually unsuitable as coatingcompositions.

Example 7 Paint Formulation and Paint

A portion of the product from Example 3 was mixed thoroughly with 3.0%of the photoinitator Darocur® 1173. Using a bone doctor blade with a gapof 90 μm, the mixture was drawn as a thin film onto a glass plate. UVirradiation (medium-pressure mercury lamp, IST Metz GmbH, Nürtingen, DE,750 mJ/cm²) gave a transparent, hard and solvent-resistant coatinghaving a Pendel hardness of 97 s, which showed no visible change after100 double rubs with a cotton pad soaked with butyl acetate.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. A process for preparing a binder which contains 1) allophanategroups, 2) groups that react with ethylenically unsaturated compoundswith polymerization on exposure to actinic radiation (radiation-curinggroups) and 3) optionally NCO-reactive groups, which comprises reactingat temperatures ≦130° C. A) one or more NCO-functional compoundscontaining uretdione groups with B) one or more compounds that containisocyanate-reactive groups and contain groups that react withethylenically unsaturated compounds with polymerization on exposure toactinic radiation (radiation-curing groups), and then with C) one ormore saturated, hydroxyl-containing compounds other than B), at leastone of these compounds having an OH functionality of ≧2, in the presenceof D) a catalyst containing one or more ammonium salts or phosphoniumsalts of aliphatic or cycloaliphatic carboxylic acids, the reaction withcompounds C) taking place at least proportionally with the formation ofallophanate groups.
 2. The process of claim 1 wherein said compoundscontaining uretdione groups are prepared from hexamethylenediisocyanate.
 3. The process of claim 1 wherein component B) comprises amember selected from the group consisting of 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene oxidemono(meth)acrylate, polypropylene oxide mono(meth)acrylate and thereaction product of acrylic acid with glycidyl methacrylate.
 4. Theprocess of claim 2 wherein component B) comprises a member selected fromthe group consisting of 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, 4-hydroxybutyl acrylate, polyethylene oxidemono(meth)acrylate, polypropylene oxide mono(meth)acrylate and thereaction product of acrylic acid with glycidyl methacrylate.
 5. Theprocess of claim 1 wherein component C) comprises a member selected fromthe group consisting of monomeric diols, monomeric triols, polyethersand polylacetones derived therefrom having a number average molecularweight of below 1000 g/mol.
 6. The process of claim 1 wherein componentD) consists essentially of zinc compounds.
 7. The process of claim 1wherein component D) comprises zinc acetylacetonate and/or zincethylhexanoate.
 8. The process of claim 2 wherein component D) compriseszinc acetylacetonate and/or zinc ethylhexanoate.
 9. The process of claim3 wherein component D) comprises zinc acetylacetonate and/or zincethylhexanoate.
 10. The process of claim 4 wherein component D)comprises zinc acetylacetonate and/or zinc ethylhexanoate.
 11. Theprocess of claim 1 wherein the reaction is carried out at a temperatureof 20 to 100° C.
 12. A binder which contains 1) allophanate groups, 2)groups that react with ethylenically unsaturated compounds withpolymerization on exposure to actinic radiation (radiation-curinggroups) and 3) optionally NCO-reactive groups, which is prepared by aprocess comprising reacting at temperatures ≦130° C. A) one or moreNCO-functional compounds containing uretdione groups with B) one or morecompounds that contain isocyanate-reactive groups and contain groupsthat react with ethylenically unsaturated compounds with polymerizationon exposure to actinic radiation (radiation-curing groups), and thenwith C) one or more saturated, hydroxyl-containing compounds other thanB), at least one of these compounds having an OH functionality of ≧2, inthe presence of D) a catalyst containing one or more zinc compounds, thereaction with compounds C) taking place at least proportionally with theformation of allophanate groups.
 13. The binder of claim 12 wherein saidcompounds containing uretdione groups are prepared from hexamethylenediisocyanate.
 14. The binder of claim 12 wherein component B) comprisesa member selected from the group consisting of 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, polyethylene oxidemono(meth)acrylate, polypropylene oxide mono(meth)acrylate and thereaction product of acrylic acid with glycidyl methacrylate.
 15. Thebinder of claim 13 wherein component B) comprises a member selected fromthe group consisting of 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, 4-hydroxybutyl acrylate, polyethylene oxidemono(meth)acrylate, polypropylene oxide mono(meth)acrylate and thereaction product of acrylic acid with glycidyl methacrylate.
 16. Thebinder of claim 12 wherein component C) comprises a member selected fromthe group consisting of monomeric diols, monomeric triols, polyethersand polylacetones derived therefrom having a number average molecularweight of below 1000 g/mol.
 17. The binder of claim 13 wherein componentC) comprises a member selected from the group consisting of monomericdiols, monomeric triols, polyethers and polylacetones derived therefromhaving a number average molecular weight of below 1000 g/mol.
 18. Thebinder of claim 15 wherein component C) comprises a member selected fromthe group consisting of monomeric diols, monomeric triols, polyethersand polylacetones derived therefrom having a number average molecularweight of below 1000 g/mol.
 19. A coating composition comprising a) oneor more of the binders of claim 8, b) optionally one or morepolyisocyanates which contain free or blocked isocyanate groups andoptionally contain groups which react with ethylenically unsaturatedcompounds with polymerization on exposure to actinic radiation, c)optionally compounds other than a) which contain groups which react withethylenically unsaturated compounds with polymerization on exposure toactinic radiation and optionally contain NCO-reactive groups, d)optionally one or more isocyanate-reactive compounds which are free fromgroups which react with ethylenically unsaturated compounds withpolymerization on exposure to actinic radiation, and e) one or moreinitiators.
 20. A substrate coated with a coating obtained from theradiation-curing binder containing allophanate groups of claim 12.